Cross cuts are cuts the go against the woodgrain. Once you've properly measured and marked your piece of wood, guide the side of the handsaw blade with the knuckle of your thumb. Start the cut by pulling your hand saw up two or three times, then push the saw blade forward at about a 45 degree angle. It is preferable to begin your cuts on the side of the wood that will show less when the project is complete.
Instead of putting a paint smear across the outside of a can to mark the level of paint left inside (which can be messy and obliterate the label), use a rubber band instead. Put it around the can and roll it down to the level of the paint. Just by glancing at the rubber band, which is visible all the way around, you will know how much paint is left.